A synchronous reluctance machine has a multiphase stator winding which is fitted to the grooves of a stator core made of magnetically conductive sheets. The stator winding forms a magnetic field which rotates at a speed defined by the electrical grid or frequency converter connected to the electrical machine. The stator winding corresponds to the stator winding of an asynchronous machine or a synchronous machine. The rotor of the synchronous reluctance machine is fitted with bearings to rotate with an air gap between the rotor and the stator.
The operation of the synchronous reluctance machine is based on an anistropic rotor structure in which each rotor pole has a direction of minimum reluctance, the d-axis, and the direction of maximum reluctance, the q-axis. The rotor's d-axis follows the peak value of the stator's rotating magnetic field. The rotor is manufactured so that the magnetic conductivity is high in the direction of the d-axis and low in the direction of the q-axis. To maximize the power and torque of the synchronous reluctance machine, the ratio of the rotor's longitudinal inductance Ld and the transverse inductance Lq ought to be as great as possible. To achieve a great inductance ratio Ld/Lq, there are several suggestions for the structure in which well-conducting routes are formed for the flux in the direction of the d-axis and flux barriers are formed to prevent the flow of magnetic flux in the direction of the q-axis.
The conductive routes of the magnetic flux are, for example, formed of ferromagnetic sheets which are fitted so that the magnetic conductivity is great in the direction of the d-axis. Air or other non-ferromagnetic material can be used as flux barriers for the magnetic flux. When using air, the mechanical durability of the rotor must be ensured with support devices.
The publications JP 2005245052 and U.S. Pat. No. 6,239,526 characterize a synchronous reluctance machine rotor in which the flux barriers are formed to the rotor by punching or cutting off parts of the rotor core sheets.
GB 1,109,974 suggests a rotor structure in which thin electric sheets with the desired direction characteristics are assembled on the axis.
Publications KR 709301 and U.S. Pat. No. 6,066,904 suggest a two-pole synchronous reluctance machine's rotor which is assembled of thin directed electric sheets. To achieve the required anisotropy of reluctance, air gaps, i.e. magnetic barriers, are formed in the laminated sheets along the magnetic flux lines in accordance with the directional characteristics.
Publication JP 11144930 suggests forming the magnetic structure by layering magnetic and non-magnetic materials which are connected to each other with a metallurgic process.
Publication WO1996042132 A1 suggests using a rotor which is made of magnetic and non-magnetic materials and has a conductive non-magnetic protective layer on it.